Many electronic and computer-related products, such as semiconductors, CD-ROMs, and computer hard disks, require highly polished surfaces in order to achieve optimum operational characteristics. For example, high-quality and extremely precise wafer surfaces are often needed during the production of semiconductor-based integrated circuits. During the fabrication process, the wafers generally undergo multiple masking, etching, and dielectric and conductor deposition processes. Because of the high-precision required in the production of these integrated circuits, an extremely flat surface is generally needed on at least one side of the semiconductor wafer to ensure proper accuracy and performance of the microelectronic structures created on the wafer surface. As the size of integrated circuits decreases and the density of microstructures on integrated circuits increases, the need for accurate and precise wafer surface polishing increases.
Chemical Mechanical Polishing (“CMP”) machines have been developed to polish or planarize semiconductor wafer surfaces to the flat condition desired for integrated circuit components and the like. For examples of conventional CMP processes and machines, see U.S. Pat. No. 4,805,348, issued Feb. 21, 1989 to Arai et al; U.S. Pat. No. 4,811,522, issued Mar. 14, 1989 to Gill; U.S. Pat. No. 5,099,614, issued Mar. 31, 1992 to Arai et al; U.S. Pat. No. 5,329,732, issued Jul. 19, 1994 to Karlsrud et al; U.S. Pat. No. 5,498,196, issued Mar. 12, 1996 to Karlsrud et al;
U.S. Pat. No. 5,498,199, issued Mar. 12, 1996 to Karlsrud et al; U.S. Pat. No. 5,558,568, issued Sep. 24, 1996 to Talieh et al; and U.S. Pat. No. 5,584,751, issued Dec. 17, 1996 to Kobayashi et al.
Typically, a CMP machine includes a wafer carrier configured to hold, rotate, and transport a wafer during the process of polishing or planarizing the wafer. During a polishing operation, a pressure-applying element (e.g., a rigid plate, a bladder assembly, or the like), which may be integral to the wafer carrier, applies pressure such that the wafer engages the polishing surface with a desired amount of force. The carrier and the polishing pad are rotated, typically at different rotational velocities, to cause relative lateral motion between the polishing pad and the wafer and to promote uniform polishing.
Commercially available polishing pads may utilize various materials, as is known in the art. The hardness and density of the polishing pad depends on the material that is to be polished and the degree of precision required in the polishing process. Typically, conventional polishing pads may be formed from a blown polyurethane, such as the IC and GS series of polishing pads available from Rodel Products Corporation in Scottsdale, Ariz.
In conventional CMP apparatus, the platens use polishing pads the entire surface of which are used to planarize each wafer, with the result that the first wafer sees a totally fresh pad while the last wafer sees a pad in glazed condition. In addition, during polishing, the polishing pad wears unevenly, developing worn tracks that result in nonuniform polishing of the wafer. In order to minimize this problem, it is well known in the art to recondition the pad between each wafer, or a certain number of wafers, being processed. However, adding the pad-reconditioning step to the wafer planarization process typically slows the throughput of the apparatus. Also, while reconditioning the pad does assist in making a used pad appear more like a fresh pad, the pad nevertheless continues to deteriorate through its life introducing a variable that alters the planarization process from wafer to wafer.
Planarization of wafers using linear belts or indexable strips are known in the art. For examples of apparatus using such planarization devices, see U.S. Pat. No. 5,335,453, issued Aug. 9, 1994 to Baldy, et al., and International Application No. PCT/US98/06844, published Oct. 15, 1998. These apparatus typically include a belt which moves linearly relative to a wafer that is urged against the belt by a wafer carrier. The wafer carrier also causes rotary or oscillating movement of the wafer against the linear belt.
While prior art devices which use orbiting wafer carriers are known, such devices pose several disadvantages. The orbiting wafer carriers may generate vibrations which create noise that adversely effects endpoint detection devices, particularly acoustic endpoint detection devices. In addition, in multi-polishing station systems, the vibration generated by one wafer carrier may translate to other neighboring wafer carriers, thereby adversely affecting uniformity of the planarization performed by the neighboring wafer carriers.
A need therefore exists for an apparatus and method of planarizing wafers that enhances the planarization of the wafers. A need further exists for an apparatus and method of planarizing wafers that allows each wafer to experience similar pad conditions as all other wafers.